WorkplaceSafety and Health Student Manual
Ordering InformationTo receive documents or other information about occupational safety andhealth topics, contact the Nati...
Student ManualJanuary 2002
Acknowledgments     This document was prepared by Thaddeus W. Fowler, Ed.D., and Karen K.     Miles, Ph.D., Education and ...
ForewordThe National Institute for Occupational Safety and Health (NIOSH) estimatesthat 200,000 young workers under the ag...
Contents                                                                                                   PageSection 1 ....
Contents (continued)                                                                                                      ...
Electrical SafetySection 1                                                                  Note to the learner—This manua...
ELECTRICITY                                         This manual will present many topics. There are four main types of    ...
I S DA N G E RO U S         energized black wire—and you are also in contact with the neu-          „ conductor—material i...
ELECTRICITY                                                 You can even receive a shock when you are not in contact with ...
I S DA N G E RO U S                                                Always test a circuit to make                          ...
DA N G E R S O F E L E                                          Section 2                                          Dangers...
CTRICAL SHOCK                                      Effects of Electrical Current* on the Body3        Current             ...
DA N G E R S O F E L                                        shock (lasting a few seconds) could be fatal if the level of c...
ECTRICAL SHOCK                     male service technician arrived at a customer’s house to perform pre-winter maintenance...
DA N G E R S O F E L                 There have been cases where an arm or leg is severely burned by                 high-...
ECTRICAL SHOCK      Summary of Section 2      The danger from electrical shock depends on • • •            the amount of t...
B U R N S C AU S E D                                          Section 3                                          Burns Cau...
BY ELECTRICITY       thermal energy, serious physical injury may result. The pressure       wave can propel large objects ...
B U R N S C AU S E D     Electrical Fires     Electricity is one of the most common     causes of fires and thermal burns ...
BY ELECTRICITY      Thermal burns may result if an explosion occurs when electricity      ignites an explosive mixture of ...
First Aid Fact Sheet What Should I Do If a Co-Worker Is Shocked or Burned by Electricity?                                t...
Once you know that electrical current is no longer flowing through the victim, call out    to the victim to see if he or s...
OV E RV I E W O F T H E                                       Section 4:                                       Overview of...
SAFETY MODEL      by someone who is reckless or dangerous. Don’t take a chance.      Careful planning of safety procedures...
OV E RV I E W O F T H EUse the safety model to recognize, evaluate, and control workplace hazards like those inthis pictur...
SAFETY MODEL      Summary of Section 4      The three stages of the safety model are • • •            Stage 1— Recognize h...
S A F E T Y M O D E L S TA G E 1                              Section 5                              Safety Model Stage 1—...
—RECOGNIZING HAZARDS                   Worker was electrocuted while removing                   energized fish tape.      ...
S A F E T Y M O D E L S TA G E 1                                            Inadequate wiring hazards„ wire gauge—wire siz...
—RECOGNIZING HAZARDS      terminals in motors, appliances, and electronic equipment may be      exposed. Older equipment m...
S A F E T Y M O D E L S TA G E 1                                                                          Shocks and elect...
—RECOGNIZING HAZARDS      Extension cords may have damaged insulation. Sometimes the insu-      lation inside an electrica...
S A F E T Y M O D E L S TA G E 1„ If you touch a defective live          electrical device that is not grounded (or ground...
—RECOGNIZING HAZARDS      The temperature of the wires can be high enough to cause a fire. If      their insulation melts,...
S A F E T Y M O D E L S TA G E 1                                        Damaged insulation, equipment, or tools can expose...
—RECOGNIZING HAZARDS        u Intensive use of hand tools that involve force or twisting can          cause tendinitis of ...
S A F E T Y M O D E L S TA G E 1                              u Low back pain can result from lifting objects the wrong wa...
—RECOGNIZING HAZARDS      Summary of Section 5      You need to be able to recognize that electrical shocks, fires, or fal...
S A F E T Y M O D E L S TA G E                                               Section 6                                    ...
2 — E VA L U AT I N G H A Z A R D S          u A cable, fuse box, or junction box that feels warm may indicate            ...
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  1. 1. WorkplaceSafety and Health Student Manual
  2. 2. Ordering InformationTo receive documents or other information about occupational safety andhealth topics, contact the National Institute for Occupational Safety andHealth (NIOSH) at NIOSH—Publications Dissemination 4676 Columbia Parkway Cincinnati, OH 45226–1998 Telephone: 1–800–35–NIOSH (1–800–356–4674) Fax number: 513–533–8573 E-mail: pubstaft@cdc.gov or visit the NIOSH Web site at www.cdc.gov/niosh This document is in the public domain and may be freely copied or reprinted. Disclaimer: Mention of any company or product does not constitute endorsement by NIOSH. DHHS (NIOSH) Publication No. 2002-123
  3. 3. Student ManualJanuary 2002
  4. 4. Acknowledgments This document was prepared by Thaddeus W. Fowler, Ed.D., and Karen K. Miles, Ph.D., Education and Information Division (EID) of the National Institute for Occupational Safety and Health (NIOSH). Editorial services were provided by John W. Diether. Pauline Elliott provided layout and design. The authors wish to thank John Palassis and Diana Flaherty (NIOSH), Robert Nester (formerly of NIOSH), and participating teachers and students for their contributions to the development of this document.ii
  5. 5. ForewordThe National Institute for Occupational Safety and Health (NIOSH) estimatesthat 200,000 young workers under the age of 18 suffer work-related injuries inthe United States each year. Young and new workers have a high risk for work-related injury compared with more experienced workers. Occupational safetyand health training remains a fundamental element of hazard control in the work-place, and there is great potential to reduce these incidents through pre-employ-ment training. Effective pre-employment training should include realistic envi-ronments and hands-on exercises. However, NIOSH recommends that actualemployment in the electrical trades or any of the other construction trades bedelayed until individuals reach the minimum age of 18.This student manual is part of a safety and health curriculum for secondary andpost-secondary electrical trades courses. The manual is designed to engage thelearner in recognizing, evaluating, and controlling hazards associated with elec-trical work. It was developed through extensive research with vocational instruc-tors, and we are grateful for their valuable contributions. Kathleen M. Rest, Ph.D., M.P.A. Acting Director National Institute for Occupational Safety and Health iii
  6. 6. Contents PageSection 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Electricity Is Dangerous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 How Is an Electrical Shock Received? . . . . . . . . . . . . . . . . . . . . . 2 Summary of Section 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Section 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Dangers of Electrical Shock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Summary of Section 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Section 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Burns Caused by Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Electrical Fires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Summary of Section 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15First Aid Fact Sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Section 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Overview of the Safety Model . . . . . . . . . . . . . . . . . . . . . . . . . . 18 What Must Be Done to Be Safe? . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Summary of Section 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Section 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Safety Model Stage 1—Recognizing Hazards . . . . . . . . . . . . . . . . . 22 How Do You Recognize Hazards? . . . . . . . . . . . . . . . . . . . . . . . . 22 Inadequate wiring hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Exposed electrical parts hazards . . . . . . . . . . . . . . . . . . . . . . . 24 Overhead powerline hazards . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Defective insulation hazards . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Improper grounding hazards . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Overload hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Wet conditions hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Additional hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Summary of Section 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Section 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Safety Model Stage 2—Evaluating Hazards . . . . . . . . . . . . . . . . . . 34 How Do You Evaluate Your Risk? . . . . . . . . . . . . . . . . . . . . . . . . 34 Summary of Section 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 v
  7. 7. Contents (continued) Page Section 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Safety Model Stage 3—Controlling Hazards: Safe Work Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 How Do You Control Hazards? . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 How Do You Create a Safe Work Environment? . . . . . . . . . . . . . . 36 Lock out and tag out circuits and equipment . . . . . . . . . . . . . . 37 Lock-out/tag-out checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Control inadequate wiring hazards . . . . . . . . . . . . . . . . . . . . . 39 Control hazards of fixed wiring . . . . . . . . . . . . . . . . . . . . . . . . 40 Control hazards of flexible wiring . . . . . . . . . . . . . . . . . . . . . . 40 Use flexible wiring properly . . . . . . . . . . . . . . . . . . . . . . . . 40 Use the right extension cord . . . . . . . . . . . . . . . . . . . . . . . . 42 Control hazards of exposed live electrical parts: isolate energized components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Control hazards of exposure to live electrical wires: use proper insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Control hazards of shocking currents . . . . . . . . . . . . . . . . . . . . 46 Ground circuits and equipment . . . . . . . . . . . . . . . . . . . . . . 46 Use GFCI’s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Bond components to assure grounding path . . . . . . . . . . . . 49 Control overload current hazards . . . . . . . . . . . . . . . . . . . . . . . 50 Summary of Section 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Section 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Safety Model Stage 3—Controlling Hazards: Safe Work Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 How Do You Work Safely? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Plan your work and plan for safety . . . . . . . . . . . . . . . . . . . . . 55 Ladder safety fact sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Avoid wet working conditions and other dangers . . . . . . . . . . . 61 Avoid overhead powerlines . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Use proper wiring and connectors . . . . . . . . . . . . . . . . . . . . . . 61 Use and maintain tools properly . . . . . . . . . . . . . . . . . . . . . . . 64 Wear correct PPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 PPE fact sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Summary of Section 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Endnotes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Index ................................................ 76 Photo and Graphics Credits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77vi
  8. 8. Electrical SafetySection 1 Note to the learner—This manual describes the hazards of electrical work and basic approaches to working safely.Electricity Is Dangerous You will learn skills to help you recognize, evaluate, and control electrical hazards.Whenever you work with power tools or on electrical circuits there This information will prepare you for addi-is a risk of electrical hazards, especially electrical shock. Anyone tional safety training such as hands-oncan be exposed to these hazards at home or at work. Workers are exercises and more detailed reviews ofexposed to more hazards because job sites can be cluttered with regulations for electrical work.tools and materials, fast-paced, and open to the weather. Risk is also Your employer, co-workers, and communityhigher at work because many jobs involve electric power tools. will depend on your expertise. Start your career off right by learning safe practices and developing good safety habits. SafetyElectrical trades workers must pay special attention to electrical haz- is a very important part of any job. Do itards because they work on electrical circuits. Coming in contact with right from the start.an electrical voltage can cause current to flow through the body,resulting in electrical shock and burns. Serious injury or even death „ Electrical shock causes injury ormay occur. As a source of energy, electricity is used without much death!thought about the hazards it can cause. Because electricity is a famil-iar part of our lives, it often is not treated with enough caution. As aresult, an average of one worker is electrocuted on the job every dayof every year! Electrocution is the third leading cause of work-related deaths among 16- and 17-year-olds, after motor vehicledeaths and workplace homicide. Electrocution is the cause of12% of all workplace deaths among young workers.1 Electrical work can be deadly if not done safely.Section 1 Page 1
  9. 9. ELECTRICITY This manual will present many topics. There are four main types of electrical injuries: electrocution (death due to electrical shock), electrical shock, burns, and falls. The dangers of electricity, electri- cal shock, and the resulting injuries will be discussed. The various electrical hazards will be described. You will learn about the Safety Model, an important tool for recognizing, evaluating, and con- trolling hazards. Important definitions and notes are shown in the margins. Practices that will help keep you safe and free of injury are emphasized. To give you an idea of the hazards caused by electricity, case studies about real-life deaths will be described.„ current—the movement of How Is an Electrical Shock Received? electrical charge„ voltage—a measure of An electrical shock is received when electrical current passes electrical force through the body. Current will pass through the body in a variety of„ circuit—a complete path for the flow situations. Whenever two wires are at different voltages, current will of current pass between them if they are connected. Your body can connect the„ You will receive a shock if you touch two wires at different wires if you touch both of them at the same time. Current will pass voltages at the same time. through your body. Wires carry current. In most household wiring, the black wires and the red wires are at„ ground—a physical electrical con- 120 volts. The white wires are at 0 volts because they are connected nection to the earth to ground. The connection to ground is often through a conducting„ energized (live, “hot”)—similar ground rod driven into the earth. The connection can also be made terms meaning that a voltage is through a buried metal water pipe. If you come in contact with an present that can cause a current, so there is a possibility of getting shockedPage 2 Section 1
  10. 10. I S DA N G E RO U S energized black wire—and you are also in contact with the neu- „ conductor—material in which an tral white wire—current will pass through your body. You will electrical current moves easily receive an electrical shock. „ neutral—at ground potential (0 volts) because of a connection to ground Metal electrical boxes should be grounded to prevent shocks. Black and red wires are usually energized, and white wires are usually neutral. If you are in contact with a live wire or any live component of an „ You will receive a shock if energized electrical device—and also in contact with any you touch a live wire and are grounded at the same time. grounded object—you will receive a shock. Plumbing is often grounded. Metal electrical boxes and conduit are grounded. „ When a circuit, electrical component, or equipment is Your risk of receiving a shock is greater if you stand in a puddle of energized, a potential shock hazard is present. water. But you don’t even have to be standing in water to be at risk. Wet clothing, high humidity, and perspiration also increase your chances of being electrocuted. Of course, there is always a chance of electrocution, even in dry conditions. Section 1 Page 3
  11. 11. ELECTRICITY You can even receive a shock when you are not in contact with an electrical ground. Contact with both live wires of a 240-volt cable will deliver a shock. (This type of shock can occur because one live wire may be at +120 volts while the other is at -120 volts during an alternating current cycle—a difference of 240 volts.). You can also receive a shock from electrical components that are not grounded properly. Even contact with another person who is receiving an elec- trical shock may cause you to be shocked. 30-year-old male electrical technician was helping a company service representative test the volt- A age-regulating unit on a new rolling mill. While the electrical technician went to get the equipment service manual, the service representative opened the panel cover of the voltage regulator’s con- trol cabinet in preparation to trace the low-voltage wiring in question (the wiring was not color-coded). The service representative climbed onto a nearby cabinet in order to view the wires. The technician returned and began working inside the control cabinet, near exposed energized electrical conductors. The techni- cian tugged at the low-voltage wires while the service representative tried to identify them from above. Suddenly, the representative heard the victim making a gurgling sound and looked down to see the victim shaking as though he were being shocked. Cardiopulmonary resuscitation (CPR) was administered to the victim about 10 minutes later. He was pronounced dead almost 2 hours later as a result of his contact with an energized electrical conductor. To prevent an incident like this, employers should take the following steps: • Establish proper rules and procedures on how to access electrical control cabinets without getting hurt. • Make sure all employees know the importance of de-energizing (shutting off) electrical systems before performing repairs. • Equip voltage-regulating equipment with color-coded wiring. • Train workers in CPR. maintenance man rode 12 feet above the floor on a motorized lift to work on a 277-volt light fixture. A He did not turn off the power supply to the lights. He removed the line fuse from the black wire, which he thought was the “hot” wire. But, because of a mistake in installation, it turned out that the white wire was the “hot” wire, not the black one. The black wire was neutral. He began to strip the white wire using a wire stripper in his right hand. Electricity passed from the “hot” white wire to the stripper, then into his hand and through his body, and then to ground through his left index finger. A co-worker heard a noise and saw the victim lying face-up on the lift. She immediately summoned another worker, who low- ered the platform. CPR was performed, but the maintenance man could not be saved. He was pronounced dead at the scene. You can prevent injuries and deaths by remembering the following points: • If you work on an electrical circuit, test to make sure that the circuit is de-energized (shut off)! • Never attempt to handle any wires or conductors until you are absolutely positive that their electrical supply has been shut off. • Be sure to lock out and tag out circuits so they cannot be re-energized. • Always assume a conductor is dangerous.Page 4 Section 1
  12. 12. I S DA N G E RO U S Always test a circuit to make sure it is de-energized before working on it. Summary of Section 1 You will receive an electrical shock if a part of your body completes an electrical circuit by • • • touching a live wire and an electrical ground, or touching a live wire and another wire at a different voltage. Section 1 Page 5
  13. 13. DA N G E R S O F E L E Section 2 Dangers of Electrical Shock The severity of injury from electrical shock depends on the amount of electrical current and the length of time the current passes „ ampere (amp)—the unit used to measure current through the body. For example, 1/10 of an ampere (amp) of elec- tricity going through the body for just 2 seconds is enough to cause death. The amount of internal current a person can withstand and still be able to control the muscles of the arm and hand can be less „ milliampere (milliamp or mA)— 1/1,000 of an ampere than 10 milliamperes (milliamps or mA). Currents above 10 mA can paralyze or “freeze” muscles. When this “freezing” happens, a „ shocking current—electrical current person is no longer able to release a tool, wire, or other object. In that passes through a part of the fact, the electrified object may be held even more tightly, resulting body in longer exposure to the shocking current. For this reason, hand- „ You will be hurt more if you can’t held tools that give a shock can be very dangerous. If you can’t let let go of a tool giving a shock. go of the tool, current continues through your body for a longer time, which can lead to respiratory paralysis (the muscles that con- trol breathing cannot move). You stop breathing for a period of „ The longer the shock, the greater time. People have stopped breathing when shocked with currents the injury. from voltages as low as 49 volts. Usually, it takes about 30 mA of current to cause respiratory paralysis. Currents greater than 75 mA cause ventricular fibrillation (very rapid, ineffective heartbeat). This condition will cause death within a few minutes unless a special device called a defibrillator is used to save the victim. Heart paralysis occurs at 4 amps, which means the heart does not pump at all. Tissue is burned with currents greater than 5 amps.2 The table shows what usually happens for a range of currents (lasting one second) at typical household voltages. Longer exposure times increase the danger to the shock victim. For example, a cur- rent of 100 mA applied for 3 seconds is as dangerous as a current of 900 mA applied for a fraction of a second (0.03 seconds). The mus- cle structure of the person also makes a difference. People with less muscle tissue are typically affected at lower current levels. Even low voltages can be extremely dangerous because the degree of injury depends not only on the amount of current but also on the length of time the body is in contact with the circuit.Defibrillator in use. LOW VOLTAGE DOES NOT MEAN LOW HAZARD! Page 6 Section 2
  14. 14. CTRICAL SHOCK Effects of Electrical Current* on the Body3 Current Reaction 1 milliamp Just a faint tingle. 5 milliamps Slight shock felt. Disturbing, but not painful. Most people can “let go.” However, strong involuntary movements can cause injuries. 6–25 milliamps (women)† Painful shock. Muscular control is lost. This is the range where “freezing 9–30 milliamps (men) currents” start. It may not be possible to “let go.” 50–150 milliamps Extremely painful shock, respiratory arrest (breathing stops), severe muscle contractions. Flexor muscles may cause holding on; extensor muscles may cause intense pushing away. Death is possible. 1,000–4,300 milliamps Ventricular fibrillation (heart pumping action not rhythmic) occurs. Muscles (1–4.3 amps) contract; nerve damage occurs. Death is likely. 10,000 milliamps Cardiac arrest and severe burns occur. Death is probable. (10 amps) 15,000 milliamps Lowest overcurrent at which a typical fuse or circuit breaker opens a circuit! (15 amps) *Effects are for voltages less than about 600 volts. Higher voltages also cause severe burns. †Differences in muscle and fat content affect the severity of shock. Sometimes high voltages lead to additional injuries. High voltages „ High voltages cause additional can cause violent muscular contractions. You may lose your balance injuries! and fall, which can cause injury or even death if you fall into machinery that can crush you. High voltages can also cause severe burns (as seen on pages 9 and 10). At 600 volts, the current through the body may be as great as 4 amps, causing damage to internal organs such as the heart. High „ Higher voltages can cause larger voltages also produce burns. In addition, internal blood vessels may currents and more severe shocks. clot. Nerves in the area of the contact point may be damaged. Muscle contractions may cause bone fractures from either the con- tractions themselves or from falls. A severe shock can cause much more damage to the body than is „ Some injuries from electrical visible. A person may suffer internal bleeding and destruction of tis- shock cannot be seen. sues, nerves, and muscles. Sometimes the hidden injuries caused by electrical shock result in a delayed death. Shock is often only the beginning of a chain of events. Even if the electrical current is too small to cause injury, your reaction to the shock may cause you to fall, resulting in bruises, broken bones, or even death. The length of time of the shock greatly affects the amount of injury. If the shock is short in duration, it may only be painful. A longer Section 2 Page 7
  15. 15. DA N G E R S O F E L shock (lasting a few seconds) could be fatal if the level of current is high enough to cause the heart to go into ventricular fibrillation. This is not much current when you realize that a small power drill uses 30 times as much current as what will kill. At relatively high currents, death is certain if the shock is long enough. However, if the shock is short and the heart has not been damaged, a normal heartbeat may resume if contact with the electrical current is elimi- nated. (This type of recovery is rare.)„ The greater the current, the The amount of current greater the shock! passing through the body also affects the severity of„ Severity of shock depends on an electrical shock. Greater voltage, amperage, and resist- ance. voltages produce greater currents. So, there is greater danger from higher voltages. Resistance hin- ders current. The lower the„ resistance—a materials ability to resistance (or impedance in decrease or stop electrical current AC circuits), the greater the current will be. Dry skin may have a resistance of 100,000 ohms or more. Wet skin may have a resistance of only 1,000 ohms. Wet working conditions or bro-„ ohm—unit of measurement for ken skin will drastically electrical resistance reduce resistance. The low resistance of wet skin Power drills use 30 times as allows current to pass into much current as what will kill. the body more easily and„ Lower resistance causes greater currents. give a greater shock. When more force is applied to the contact point or when the contact area is larger, the resistance is lower, causing stronger shocks. The path of the electrical current through the body affects the severi- ty of the shock. Currents through the heart or nervous system are most dangerous. If you contact a live wire with your head, your nerv- ous system will be damaged. Contacting a live electrical part with one hand—while you are grounded at the other side of your body—„ Currents across the chest are very will cause electrical current to pass across your chest, possibly injur- dangerous. ing your heart and lungs.Page 8 Section 2
  16. 16. ECTRICAL SHOCK male service technician arrived at a customer’s house to perform pre-winter maintenance on an oil A furnace. The customer then left the house and returned 90 minutes later. She noticed the service truck was still in the driveway. After 2 more hours, the customer entered the crawl space with a flashlight to look for the technician but could not see him. She then called the owner of the company, who came to the house. He searched the crawl space and found the technician on his stomach, leaning on his elbows in front of the furnace. The assistant county coroner was called and pronounced the technician dead at the scene. The victim had electrical burns on his scalp and right elbow. After the incident, an electrician inspected the site. A toggle switch that supposedly controlled electrical power to the furnace was in the “off” position. The electrician described the wiring as “haphazard and confusing.” Two weeks later, the county electrical inspector performed another inspection. He discovered that incor- rect wiring of the toggle switch allowed power to flow to the furnace even when the switch was in the “off” position. The owner of the company stated that the victim was a very thorough worker. Perhaps the victim performed more maintenance on the furnace than previous technicians, exposing himself to the electrical hazard. This death could have been prevented! • The victim should have tested the circuit to make sure it was de-energized. • Employers should provide workers with appropriate equipment and training. Using safety equipment should be a requirement of the job. In this case, a simple circuit tester may have saved the victim’s life. • Residential wiring should satisfy the National Electrical Code (NEC). Although the NEC is not retroac- tive, all homeowners should make sure their systems are safe. „ NEC—National Electrical Code— a comprehensive listing of practices to protect workers and equipment from electrical hazards such as fire and electrocution Electrical burn on hand and arm. Section 2 Page 9
  17. 17. DA N G E R S O F E L There have been cases where an arm or leg is severely burned by high-voltage electrical current to the point of coming off, and the victim is not electrocuted. In these cases, the current passes through only a part of the limb before it goes out of the body and into another conductor. Therefore, the current does not go through the chest area and may not cause death, even though the victim is severely disfig- ured. If the current does go through the chest, the person will almost surely be electrocuted. A large number of serious electrical injuries involve current passing from the hands to the feet. Such a path involves both the heart and lungs. This type of shock is often fatal. Arm with third degree burn from high-voltage line.Page 10 Section 2
  18. 18. ECTRICAL SHOCK Summary of Section 2 The danger from electrical shock depends on • • • the amount of the shocking current through the body, the duration of the shocking current through the body, and the path of the shocking current through the body. Section 2 Page 11
  19. 19. B U R N S C AU S E D Section 3 Burns Caused by Electricity The most common shock-related, nonfatal injury is a burn. Burns„ Electrical shocks cause burns. caused by electricity may be of three types: electrical burns, arc burns, and thermal contact burns. Electrical burns can result when a person touches electrical wiring or equipment that is used or main- tained improperly. Typically, such burns occur on the hands. Electrical burns are one of the most serious injuries you can receive. They need to be given immediate attention. Additionally, clothing may catch fire and a„ arc-blast—explosive release of molten material from equipment caused by thermal burn may result from the high-amperage arcs heat of the fire. Contact electrical burns. The knee on the left was energized, Arc-blasts occur when powerful, and the knee on the right was high-amperage currents arc grounded. through the air. Arcing is the„ arcing—the luminous electrical dis- charge (bright, electrical sparking) luminous electrical discharge that occurs when high voltages exist through the air that occurs when high across a gap between conductors and current travels through the air. voltages exist across a gap between This situation is often caused by equipment failure due to abuse or conductors fatigue. Temperatures as high as 35,000°F have been reached in arc-blasts. There are three primary hazards associated with an arc-blast. (1) Arcing gives off thermal radiation (heat) and intense light, which can cause burns. Several factors affect the degree of injury, includ- ing skin color, area of skin exposed, and type of clothing worn. Proper clothing, work distances, and overcurrent protection can reduce the risk of such a burn. (2) A high-voltage arc can produce a considerable pressure wave blast. A person 2 feet away from a 25,000-amp arc feels a force of about 480 pounds on the front of the body. In addition, such an explosion can cause serious ear damage and memory loss due to concussion. Sometimes the pressure wave throws the victim away from the arc-blast. While this may reduce further exposure to thePage 12 Section 3
  20. 20. BY ELECTRICITY thermal energy, serious physical injury may result. The pressure wave can propel large objects over great distances. In some cases, the pressure wave has enough force to snap off the heads of steel bolts and knock over walls. (3) A high-voltage arc can also cause many of the copper and alu- minum components in electrical equipment to melt. These droplets of molten metal can be blasted great distances by the pressure wave. Although these droplets harden rapidly, they can still be hot enough to cause serious burns or cause ordinary clothing to catch fire, even if you are 10 feet or more away. ive technicians were performing preventive maintenance on the electrical system of a railroad main- F tenance facility. One of the technicians was assigned to clean the lower compartment of an electri- cal cabinet using cleaning fluid in an aerosol can. But, he began to clean the upper compartment as well. The upper compartment was filled with live circuitry. When the clean- ing spray contacted the live circuitry, a conductive path for the current was created. The current passed through the stream of fluid, into the technician’s arm, and across his chest. The current caused a loud explosion. Co-workers found the victim with his clothes on fire. One worker put out the fire with an extinguisher, and another pulled the vic- tim away from the compartment with a plastic vacuum cleaner hose. The paramedics responded in 5 minutes. Although the victim sur- vived the shock, he died 24 hours later of burns. This death could have been prevented if the following precautions had been taken: • Before doing any electrical work, de-energize all circuits and equipment, perform lock-out/tag-out, and test circuits and equipment to make sure they are de-energized. • The company should have trained the workers to perform their jobs safely. • Proper personal protective equipment (PPE) should always be used. • Never use aerosol spray cans around high-voltage equipment. Section 3 Page 13
  21. 21. B U R N S C AU S E D Electrical Fires Electricity is one of the most common causes of fires and thermal burns in homes and workplaces. Defective or misused electrical equipment is a major cause of electrical fires. If there is a small electrical fire, be sure to use only a Class C or multi- purpose (ABC) fire extinguisher, or you might make the problem worse. All fire extinguishers are marked with letter(s) that tell you the kinds of fires they can put out. Some extinguishers contain symbols, too. The letters and symbols are explained below (including suggestions on how to remember them). A (think: Ashes) = paper, wood, etc. B (think: Barrel) = flammable liquids C (think: Circuits) = electrical fires Here are a couple of fire extinguishers at a worksite. Can you tell what types of fires they will put out? This extinguisher can only This extinguisher can only be used on Class B and be used on Class A and Class C fires. Class C fires. Learn how to use fire However, do not try to put out fires unless you have received extinguishers at work. proper training. If you are not trained, the best thing you can do is evacuate the area and call for help.14 Section 3
  22. 22. BY ELECTRICITY Thermal burns may result if an explosion occurs when electricity ignites an explosive mixture of material in the air. This ignition can result from the buildup of combustible vapors, gasses, or dusts. Occupational Safety and Health Administration (OSHA) standards, „ OSHA—Occupational Safety and the NEC, and other safety standards give precise safety requirements Health Administration—the Federal agency in the U.S. Department of for the operation of electrical systems and equipment in such dan- Labor that establishes and enforces gerous areas. Ignition can also be caused by overheated conductors workplace safety and health or equipment, or by normal arcing at switch contacts or in circuit regulations breakers. Summary of Section 3 Burns are the most common injury caused by electricity. The three types of burns are • • • electrical burns, arc burns, and thermal contact burns. Section 3 Page 15
  23. 23. First Aid Fact Sheet What Should I Do If a Co-Worker Is Shocked or Burned by Electricity? the electrical current if the victim is still in contactShut off with the energized circuit. While you do this, have someone else call for help. If you cannot get to theswitchgear quickly, pry the victim from the circuit with something that does notconduct electricity such as dry wood. Do not touch the victim yourself if he orshe is still in contact with an electrical circuit! You do not want to be a victim, too!Do not leave the victim unless there is absolutely no other option. You should staywith the victim while Emergency Medical Services (EMS) is contacted. The callershould come back to you afterwards to verify that the call was made. If the victim isnot breathing, does not have a heartbeat, or is badly injured, quick response by ateam of emergency medical technicians (EMT’s) or paramedics gives the best chancefor survival. Learn first aidPage 16
  24. 24. Once you know that electrical current is no longer flowing through the victim, call out to the victim to see if he or she is conscious (awake). If the victim is conscious, tell the victim not to move. It is possible for a shock victim to be seriously injured but not realize it. Quickly examine the victim for signs of major bleeding. If there is a lot of bleeding, place a cloth (such as a handkerchief or bandanna) over the wound and apply pressure. If the wound is in an arm or leg and keeps bleed- ing a lot, gently elevate the injured area while keeping pressure on the wound. Keep the victim warm and talk to him or her until help arrives. If the victim is unconscious, check for signs of breathing. While you do this, move the victim as little as possible. If the victim is not breathing, someone trained in CPR should begin artificial breathing, then check to see if the victim has a pulse. Quick action is essential! To be effective, CPR must be performed within 4 minutes of the shock. If you are not trained in CPR or first aid, now is the time to get trained—before you find yourself in this situation! Ask your instructor or supervisor how you can become certified in CPR. You also need to know the location of (1) electricity shut-offs (“kill switches”), (2) first-aid sup- plies, and (3) a telephone so you can find them quickly in an emergency.and CPR now! Page 17
  25. 25. OV E RV I E W O F T H E Section 4: Overview of the Safety Model What Must Be Done to Be Safe?„ Use the safety model to recognize, Use the three-stage safety model: recognize, evaluate, and control evaluate, and control hazards. hazards. To be safe, you must think about your job and plan for hazards. To avoid injury or death, you must understand and recognize hazards. You need to evaluate the situation you are in and assess your risks. You need to control haz- ards by creating a safe work environment, by using safe work practices, and by report- ing hazards to a supervisor or teacher. If you do not recognize, evalu- ate, and control hazards, you may be injured or killed by the electricity itself, electrical fires, or falls. If you use the Report hazards to your supervisor safety model to recognize, or teacher. evaluate, and control hazards, you are much safer.„ Identify electrical hazards. (1) Recognize hazards The first part of the safety model is recognizing the hazards around you. Only then can you avoid or control the hazards. It is best to discuss and plan hazard recognition tasks with your co-workers.„ Don’t listen to reckless, Sometimes we take risks ourselves, but when we are responsible for dangerous people. others, we are more careful. Sometimes others see hazards that we overlook. Of course, it is possible to be talked out of our concernsPage 18 Section 4
  26. 26. SAFETY MODEL by someone who is reckless or dangerous. Don’t take a chance. Careful planning of safety procedures reduces the risk of injury. Decisions to lock out and tag out circuits and equipment need to be made during this part of the safety model. Plans for action must be made now. OSHA regulations, the NEC, and the National Electrical Safety Code (NESC) provide a wide range of safety information. Although these sources may be difficult to read and understand at first, with practice they can become very useful tools to help you recognize unsafe conditions and practices. Knowledge of OSHA standards is an important part of training for electrical apprentices. See the Appendix for a list of relevant standards. Always lock out and tag out circuits. (2) Evaluate hazards When evaluating hazards, it is best to identify all possible hazards „ Evaluate your risk. first, then evaluate the risk of injury from each hazard. Do not assume the risk is low until you evaluate the hazard. It is dangerous to overlook hazards. Job sites are especially dangerous because they are always changing. Many people are working at different tasks. Job sites are frequently exposed to bad weather. A reasonable place to work on a bright, sunny day might be very hazardous in the rain. The risks in your work environment need to be evaluated all the time. Then, whatever hazards are present need to be controlled. (3) Control hazards Once electrical hazards have been recognized and evaluated, they „ Take steps to control hazards: must be controlled. You control electrical hazards in two main ways: Create a safe workplace. Work safely. (1) create a safe work environment and (2) use safe work practices. Controlling electrical hazards (as well as other hazards) reduces the risk of injury or death. Section 4 Page 19
  27. 27. OV E RV I E W O F T H EUse the safety model to recognize, evaluate, and control workplace hazards like those inthis picture.Page 20 Section 4
  28. 28. SAFETY MODEL Summary of Section 4 The three stages of the safety model are • • • Stage 1— Recognize hazards Stage 2— Evaluate hazards Stage 3— Control hazards Section 4 Page 21
  29. 29. S A F E T Y M O D E L S TA G E 1 Section 5 Safety Model Stage 1— Recognizing Hazards How Do You Recognize Hazards? The first step toward protecting yourself is recognizing the many hazards you face on the job. To do this, you must know which situa- tions can place you in danger. Knowing where to look helps you to recognize hazards. u Inadequate wiring is dangerous. u Exposed electrical parts are dangerous.„ Workers face many hazards on the job. u Overhead powerlines are dangerous. u Wires with bad insulation can give you a shock. u Electrical systems and tools that are not grounded or double-insu- lated are dangerous. u Overloaded circuits are dangerous. u Damaged power tools and equipment are electrical hazards. u Using the wrong PPE is dangerous. u Using the wrong tool is dangerous. u Some on-site chemicals are harmful. u Defective ladders and scaffolding are dangerous. u Ladders that conduct electricity are dangerous. u Electrical hazards can be made worse if the worker, location, or equipment is wet.Page 22 Section 5
  30. 30. —RECOGNIZING HAZARDS Worker was electrocuted while removing energized fish tape. n electrician was removing a metal fish tape from a hole at the base of a metal light pole. (A A fish tape is used to pull wire through a conduit run.) The fish tape became energized, electro- cuting him. As a result of its inspection, OSHA issued a citation for three serious violations of the agency’s construction standards. If the following OSHA requirements had been followed, this death could have been prevented. • De-energize all circuits before beginning work. • Always lock out and tag out de-energized equipment. • Companies must train workers to recognize and avoid unsafe conditions associ- ated with their work. Fish tape. Section 5 Page 23
  31. 31. S A F E T Y M O D E L S TA G E 1 Inadequate wiring hazards„ wire gauge—wire size or diameter An electrical hazard exists when the wire is too small a gauge for the (technically, the cross-sectional area) current it will carry. Normally, the circuit breaker in a circuit is matched to the wire size. However, in older wiring, branch lines to permanent ceiling light fixtures could be wired with a smaller gauge than the supply cable. Let’s say a light fixture is replaced with another„ ampacity—the maximum amount device that uses more current. The current capacity (ampacity) of the of current a wire can carry safely branch wire could be exceeded. When a wire is too small for the cur- without overheating rent it is supposed to carry, the wire will heat up. The heated wire„ Overloaded wires get hot! could cause a fire. When you use an extension cord, the size of the wire you are plac- ing into the circuit may be too small for the equipment. The circuit breaker could be the right size for the circuit but not right for the smaller-gauge extension cord. A tool plugged into the extension cord may use more current than the cord can handle without tripping the circuit breaker. The wire will overheat and could cause a fire. The kind of metal used as a conductor can cause an electrical hazard. Special care needs to be taken with aluminum wire. Since it is more brittle than copper, aluminum wire can crack and break more easily. Connections with aluminum wire can become loose and oxidize if not made properly, creating heat or arcing. You„ Incorrect wiring practices can need to recognize that inade- cause fires! quate wiring is a hazard. Exposed electrical parts hazards Electrical hazards exist when wires or other electrical parts are exposed. Wires and parts can be exposed if a cover is removed from a wiring or breaker box. The overhead wires coming into a home may be exposed. Electrical„ If you touch live electrical parts, This hand-held sander has you will be shocked. exposed wires and should not be used.Page 24 Section 5
  32. 32. —RECOGNIZING HAZARDS terminals in motors, appliances, and electronic equipment may be exposed. Older equipment may have exposed electrical parts. If you contact exposed live electrical parts, you will be shocked. You need to recognize that an exposed electrical component is a hazard. Overhead powerline hazards „ Overhead powerlines kill many workers! Most people do not realize that overhead powerlines are usually not insulated. More than half of all electrocutions are caused by direct worker contact with energized powerlines. Powerline workers must be especially aware of the dangers of overhead lines. In the past, 80% of all lineman deaths were caused by contacting a live wire with a bare hand. Due to such incidents, all linemen now wear spe- cial rubber gloves that protect them up to 34,500 volts. Today, most electrocutions involving overhead powerlines are caused by failure to maintain proper work distances. Watch out for exposed electrical wires around Electrical line workers need special training electronic equipment. and equipment to work safely. Section 5 Page 25
  33. 33. S A F E T Y M O D E L S TA G E 1 Shocks and electrocutions occur where physical barriers are not in place to prevent contact with the wires. When dump trucks, cranes, work platforms, or other conductive materials (such as pipes and ladders) contact overhead wires, the equipment operator or other workers can be killed. If you do not maintain required clearance distances from powerlines, you can be shocked and killed. (The minimum distance for voltages up to 50kV is 10 feet. For voltages over 50kV, the minimum distance is 10 feet plus 4 inches for every 10 kV over 50kV.) Never store materials and equipment under or near over- head powerlines. You need to recognize thatOperating a crane near overhead wires is overhead powerlines are a hazard.very hazardous. ive workers were constructing a chain-link fence in front of a F house, directly below a 7,200-volt energized powerline. As they prepared to install 21-foot sections of metal top rail on the fence, one of the workers picked up a section of rail and held it up vertically. The rail contacted the 7,200-volt line, and the worker was electrocuted. Following inspection, OSHA determined that the employee who was killed had never received any safety training from his employer and no specific instruction on how to avoid the hazards associated with overhead powerlines. In this case, the company failed to obey these regulations: • Employers must train their workers to recognize and avoid unsafe conditions on the job. • Employers must not allow their workers to work near any part of an electrical circuit UNLESS the circuit is de-energized (shut off) and grounded, or guarded in such a way that it cannot be con- tacted. • Ground-fault protection must be provided at construction sites to guard against electrical shock. Defective insulation hazards Insulation that is defective or inadequate is an electrical hazard. Usually, a plastic or rubber covering insulates wires. Insulation prevents conductors from coming in contact with each„ insulation—material that does not conduct electricity easily other. Insulation also prevents conductors from coming in contact with people.Page 26 Section 5
  34. 34. —RECOGNIZING HAZARDS Extension cords may have damaged insulation. Sometimes the insu- lation inside an electrical tool or appliance is damaged. When insula- tion is damaged, exposed metal parts may become energized if a live wire inside touches them. Electric hand tools that are old, damaged, or misused may have damaged insulation inside. If „ If you touch a damaged live power you touch damaged power tools tool, you will be shocked! or other equipment, you will receive a shock. You are more likely to receive a shock if the „ A damaged live power tool that is tool is not grounded or double- not grounded or double-insulated insulated. (Double-insulated is very dangerous! tools have two insulation barri- ers and no exposed metal parts.) You need to recognize that defective insulation is a hazard. This extension cord is damaged and should not be used. Improper grounding hazards When an electrical system is not grounded properly, a hazard exists. The most common OSHA electrical violation is improper grounding of equipment and circuitry. The metal parts of an electrical wiring system that we touch (switch plates, ceiling light fixtures, conduit, etc.) should be grounded and at 0 volts. If the system is not grounded properly, these parts may become energized. Metal parts of motors, appliances, or electronics that are plugged into improperly grounded circuits may be energized. When a circuit is not grounded properly, a hazard exists because unwanted voltage cannot be safely eliminated. „ fault current—any current that is not If there is no safe path to ground for fault currents, exposed metal in its intended path parts in damaged appliances can become energized. Extension cords may not provide a continuous path to ground „ ground potential—the voltage a because of a broken ground wire or plug. If you contact a defective grounded part should have; 0 volts relative to ground Section 5 Page 27
  35. 35. S A F E T Y M O D E L S TA G E 1„ If you touch a defective live electrical device that is not grounded (or grounded improperly), you component that is not grounded, will be shocked. You need to recognize that an improperly grounded you will be shocked. electrical system is a hazard. Electrical systems are often grounded to metal water pipes that serve as a continuous path to ground. If plumbing is used as a path to ground for fault current, all pipes must be made of conductive material (a type of metal). Many electrocutions and fires occur because (during renova- tion or repair) parts of metal plumbing are replaced with plastic pipe, which does not conduct electricity. In these cases, the path to ground is interrupted by nonconductive material.„ GFCI—ground fault circuit A ground fault circuit interrupter, or GFCI, is an inexpensive life- interrupter—a device that detects saver. GFCI’s detect any difference in current between the two circuit current leakage from a circuit to wires (the black wires and white wires). This differ- ground and shuts the current off ence in current could happen when electrical equipment is not working correctly,„ leakage current—current that does causing leakage current. If leakage not return through the intended path current (a ground fault) is detected in a GFCI receptacle. but instead "leaks” to ground GFCI-protected circuit, the GFCI switches„ ground fault—a loss of current from a circuit to a ground connection off the current in the circuit, protecting you from a dangerous shock. GFCI’s are set at about 5 mA and are designed to protect workers from electrocution. GFCI’s are able to detect the loss of current resulting from leakage through a person who is beginning to be shocked. If this situation occurs, the GFCI switches off the current in the circuit. GFCI’s are different from circuit breakers because they detect leakage currents rather than overloads. Circuits with missing, damaged, or improperly wired GFCI’s may allow you to be shocked. You need to recognize that a circuit improperly protected by a GFCI is a hazard. Overload hazards„ overload—too much current in a circuit Overloads in an electrical system are hazardous because they can produce heat or arcing. Wires and other components„ An overload can lead to a fire or in an electrical system or circuit have a electrical shock. maximum amount of current they can carry safely. If too many devices are plugged into a circuit, the electrical cur- rent will heat the wires to a very high temperature. If any one tool uses too Overloads are a major cause much current, the wires will heat up. of fires.Page 28 Section 5
  36. 36. —RECOGNIZING HAZARDS The temperature of the wires can be high enough to cause a fire. If their insulation melts, arcing may occur. Arcing can cause a fire in the area where the overload exists, even inside a wall. „ circuit breaker—an overcurrent In order to prevent too much current in a circuit, a circuit breaker or protection device that automatically shuts off the current in a circuit if an fuse is placed in the circuit. If there is too much current in the cir- overload occurs cuit, the breaker “trips” and opens like a switch. If an overloaded „ trip—the automatic opening circuit is equipped with a fuse, an internal part of the fuse melts, (turning off) of a circuit by a GFCI or opening the circuit. Both breakers and fuses do the same thing: open circuit breaker the circuit to shut off the electrical current. „ fuse—an overcurrent protection If the breakers or fuses are too big for the wires they are supposed to device that has an internal part that protect, an overload in the circuit will not be detected and the cur- melts and shuts off the current in a rent will not be shut off. Overloading leads to overheating of circuit circuit if there is an overload components (including wires) and may cause a fire. You need to „ Circuit breakers and fuses that recognize that a circuit with improper overcurrent protection are too big for the circuit are dangerous. devices—or one with no overcurrent protection devices at all— „ Circuits without circuit breakers or is a hazard. fuses are dangerous. Overcurrent protection devices are built into the wiring of some electric motors, tools, and electronic devices. For example, if a tool draws too much current or if it overheats, the current will be shut off from within the device itself. Damaged tools can overheat and cause „ Damaged power tools can cause a fire. You need to recognize that a damaged tool is a hazard. overloads. Damaged equipment can overheat and cause a fire. Wet conditions hazards Working in wet conditions is hazardous because you may become an easy path for electrical current. If you touch a live wire or other „ Wet conditions are dangerous. electrical component—and you are well-grounded because you are standing in even a small puddle of water—you will receive a shock. Section 5 Page 29
  37. 37. S A F E T Y M O D E L S TA G E 1 Damaged insulation, equipment, or tools can expose you to live electrical parts. A damaged tool may not be grounded properly, so the housing of the tool may be energized, causing you to receive a shock. Improperly grounded metal switch plates and ceiling lights are especially hazardous in wet conditions. If you touch a live elec- trical component with an uninsulated hand tool, you are more likely to receive a shock when standing in water. But remember: you don’t have to be standing in water to be electro- cuted. Wet clothing, high humidity, and perspiration also increase your chances of being electrocuted. You need to recognize that all wet conditions are hazards.„ An electrical circuit in a damp place without a GFCI is dangerous! A GFCI reduces the danger. Additional hazards In addition to electrical hazards, other types of hazards are present at job sites. Remember that all of these hazards can be controlled.„ There are non-electrical hazards at job sites, too. u There may be chemical hazards. Solvents and other substances may be poisonous or cause disease. u Frequent overhead work can cause tendinitis (inflammation) in your shoulders. Overhead work can cause long-term shoulder pain.Page 30 Section 5
  38. 38. —RECOGNIZING HAZARDS u Intensive use of hand tools that involve force or twisting can cause tendinitis of the hands, wrists, or elbows. Use of hand tools can also cause carpal tunnel syndrome, which results when nerves in the wrist are damaged by swelling tendons or contract- ing muscles. Frequent use of some hand tools can cause wrist problems such as carpal tunnel syndrome. 22-year-old carpenter’s apprentice was killed when he was struck in the head by a nail A fired from a powder-actuated nail gun (a device that uses a gun powder cartridge to drive nails into concrete or steel). The nail gun operator fired the gun while attempting to anchor a plywood concrete form, causing the nail to pass through the hollow form. The nail traveled 27 feet before striking the victim. The nail gun operator had never received training on how to use the tool, and none of the employees in the area was wearing PPE. In another situation, two workers were building a wall while remodeling a house. One of the workers was killed when he was struck by a nail fired from a powder-actuated nail gun. The tool operator who fired the nail was trying to attach a piece of plywood to a wooden stud. But the nail shot though the plywood and stud, striking the victim. Below are some OSHA regulations that should have been followed. • Employees using powder- or pressure-actuated tools must be trained to use them safely. „PPE—personal protective • Employees who operate powder- or pressure-actuated tools must be trained to avoid firing equipment (eye protection, into easily penetrated materials (like plywood). hard hat, special clothing, • In areas where workers could be exposed to flying nails, appropriate PPE must be used. etc.) Section 5 Page 31
  39. 39. S A F E T Y M O D E L S TA G E 1 u Low back pain can result from lifting objects the wrong way or carrying heavy loads of wire or other material. Back pain can also occur as a result of injury from poor working surfaces such as wet or slippery floors. Back pain is common, but it can be dis- abling and can affect young individuals. u Chips and particles flying from tools can injure your eyes. Wear eye protection. u Falling objects can hit you. Wear a hard hat. u Sharp tools and power equipment can cause cuts and other injuries. If you receive a shock, you may react and be hurt by a tool. u You can be injured or killed by falling from a ladder or scaffold- ing. If you receive a shock—even a mild one—you may lose your balance and fall. Even without being shocked, you could Lift with your legs, not fall from a ladder or scaffolding. your back! u You expose yourself to hazards when you do not wear PPE. All of these situations need to be recognized as hazards. You need to be especially careful when working on scaffolding or ladders.Page 32 Section 5
  40. 40. —RECOGNIZING HAZARDS Summary of Section 5 You need to be able to recognize that electrical shocks, fires, or falls result from these hazards: Inadequate wiring Exposed electrical parts Overhead powerlines Defective insulation Improper grounding Overloaded circuits Wet conditions Damaged tools and equipment Improper PPE Section 5 Page 33
  41. 41. S A F E T Y M O D E L S TA G E Section 6 Safety Model Stage 2— Evaluating Hazards How Do You Evaluate Your Risk? „ risk—the chance that injury or After you recognize a hazard, your next step is to evaluate your risk death will occur from the hazard. Obviously, exposed wires should be recognized as a hazard. If the exposed wires are 15 feet off the ground, your risk is low. However, if you are going to be working on a roof near those same wires, your risk is high. The risk of shock is greater if you will be carrying metal conduit that could touch the exposed wires. You „ Make the right decisions. must constantly evaluate your risk. Combinations of hazards increase your risk. Improper grounding and a damaged tool greatly increase your risk. Wet conditions com- bined with other hazards also increase your risk. You will need to make decisions about the nature of hazards in order to evaluate your risk and do the right thing to remain safe. There are “clues” that electrical hazards exist. For example, if a GFCI keeps tripping while you are using a power tool, there is a problem. Don’t keep resetting the GFCI and continue to work. You must evaluate the “clue” and decide what action should be taken to control the hazard. There are a number of other conditions that indi-Combinations of hazards increase risk. cate a hazard. u Tripped circuit breakers and blown fuses show that too much „ short—a low-resistance path current is flowing in a circuit. This condition could be due to sev- between a live wire and the eral factors, such as malfunctioning equipment or a short between ground, or between wires at conductors. You need to determine the cause in order to control different voltages (called a fault if the current is unintended) the hazard. u An electrical tool, appliance, wire, or connection that feels warm may indicate too much current in the circuit or equipment. You need to evaluate the situation and determine your risk. u An extension cord that feels warm may indicate too much current for the wire size of the cord. You must decide when action needs to be taken. Page 34 Section 6
  42. 42. 2 — E VA L U AT I N G H A Z A R D S u A cable, fuse box, or junction box that feels warm may indicate Any of these conditions, or too much current in the circuits. “clues,” tells you something important: there is a risk of fire u A burning odor may indicate overheated insulation. and electrical shock. The equip- u Worn, frayed, or damaged insulation around any wire or other ment or tools involved must be conductor is an electrical hazard because the conductors could be avoided. You will frequently be exposed. Contact with an exposed wire could cause a shock. caught in situations where you Damaged insulation could cause a short, leading to arcing or a need to decide if these clues are fire. Inspect all insulation for scrapes and breaks. You need to present. A maintenance electri- evaluate the seriousness of any damage you find and decide how cian, supervisor, or instructor to deal with the hazard. needs to be called if there are signs of overload and you are not u A GFCI that trips indicates there is current leakage from the cir- sure of the degree of risk. Ask for cuit. First, you must decide the probable cause of the leakage by help whenever you are not sure recognizing any contributing hazards. Then, you must decide what to do. By asking for help, you what action needs to be taken. will protect yourself and others. Summary of Section 6 Look for “clues” that hazards are present. Evaluate the seriousness of hazards. Decide if you need to take action. Don’t ignore signs of trouble. n 18-year-old male worker, with 15 months of experience at a fast food restaurant, was plugging a toast- A er into a floor outlet when he received a shock. Since the restaurant was closed for the night, the floor had been mopped about 10 minutes before the incident. The restaurant manager and another employee heard the victim scream and investigated. The victim was found with one hand on the plug and the other hand grasping the metal receptacle box. His face was pressed against the top of the outlet. An employee tried to take the victim’s pulse but was shocked. The manager could not locate the correct breaker for the circuit. He then called the emergency squad, returned to the breaker box, and found the correct breaker. By the time the circuit was opened (turned off), the victim had been exposed to the current for 3 to 8 minutes. The employee checked the victim’s pulse again and found that it was very rapid. The manager and the employee left the victim to unlock the front door and place another call for help. Another employee arrived at the restaurant and found that the victim no longer had a pulse. The employee began administering CPR, which was continued by the rescue squad for 90 minutes. The victim was dead on arrival at a local hospital. Later, two electricians evaluated the circuit and found no serious problems. An investigation showed that the victim’s hand slipped forward when he was plugging in the toaster. His index finger made contact with an energized prong in the plug. His other hand was on the metal receptacle box, which was grounded. Current entered his body through his index finger, flowed across his chest, and exited through the other hand, which was in contact with the grounded receptacle. To prevent death or injury, you must recognize hazards and take the right action. • If the circuit had been equipped with a GFCI, the current would have been shut off before injury occurred. • The recent mopping increased the risk of electrocution. Never work in wet or damp areas! Section 6 Page 35

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